Wax nostalgic about and learn from the history of early electronics.
See articles from Radio-Craft,
published 1929 - 1953. All copyrights are hereby acknowledged.

RCA Victor was one of
America's leaders in electronic design for military, commercial, industrial, and
domestic products. The company led the way for many innovative features in reception and
sound quality, as well as customer convenience features like self-tuning and pushbutton
selection of bands and channels. The Model 9T and Model 9K2, a tabletop and a floor
console design, respectively, were virtually the same electronically with the exception of
a smaller speaker in the 9T. RCA included a "Magic Eye" for tuning as well as a "Magic
Brain" IF section for providing enhanced frequency discrimination between bands. The
"Magic Voice" setup assured that "low tones emerge in phase, and thereby eliminate boominess,
or reverberation." Wow, the 9T / 9K2 really must have been truly magic, at least
according to RCA.

The 9K2 cabinet with back open shown by reflection.
At the bottom, "Magic Voice" tubes preventing low-note resonance.

The two models are alike in all but cabinet and reproducer; 9T, table type, has an 8-in.
speaker; 9K2, console type, with 12-in. speaker, incorporates the "Magic Voice." 5 metal open-end
tubes inserted in the cabinet base, to make low tones emerge in phase, and thereby eliminate
boominess, or reverberation. (The model 9K2 is illustrated.)

An unusual method of switching is used in the antenna and detector circuits, by which parts
of the same windings are used in more than one range; the oscillator stage, for greater stability,
uses separate windings. Thus coil "X" is part of the secondary, in the X band, and "X Pri."
transmits the input signal; in the "A" band, "X" becomes the primary, leaving "A", "B", "C"
in the secondary; etc. For band D, a separate L-turn coil is used. Consult switching details
above and coil connections shown (right). The I.F. transformers are new "magnetite" type,
with fixed condensers, and tuned by adjusting the cores to obtain correct inductance. Magnetite­core
wavetrap L1 cuts out 460-kc. interference.

"Music-Speech" control is an addition to the tone-filter (on Vol. Con.) which balances
tones at different settings; Sw.5 (on power Sw.4) cuts in additional 0.1-mf. capacity to reduce
L.F. response and increase intelligibility of speech. This is in addition to regular "Tone
Control" over the output of V7.

"Magic Eye" tube, VB, with maximum volt­age (developed by 0.22-meg. resistor across input
of V5) shows resonance to signal tuned-in by minimum width of dark area on its fluorescent
end. Tuning knob has 20:1 and 100:1 dial-drive ratios, latter for the shorter waves especially.

Posted August 17, 2017

Radio Service Data Sheets

These schematics, tuning instructions, and other data are reproduced from my collection
of vintage radio and electronics magazines. As back in the era, similar schematic and service
info was available for purchase from sources such as
SAMS Photofacts, but these printings
were a no-cost bonus for readers. There are 220 Radio Service Data Sheets as of
February 2, 2018.

RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling
2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas
and reference material while performing my work as an RF system and circuit design engineer.
The Internet was still largely an unknown entity at the time and not much was available
in the form of WYSIWYG
...

All trademarks, copyrights, patents, and other rights of ownership to images and text
used on the RF Cafe website are hereby acknowledged.